1. Field of the Invention
The present invention relates to the use of a combination of halogen-free flame retardant additives in a copolyester to improve the flame retardant properties of the copolyester composition while retaining impact properties. More specifically, the present invention relates to the use of a nitrogen containing flame retardant and a metal phosphinate in copolyesters to improve the flame retardant properties while retaining impact properties.
2. Background
Flame retardant materials are added to some polymers to improve flame resistance, particularly to meet specific fire standards such as UL94 V0 or Class A according to ASTM-E-84. However, the addition of flame retardant materials in amount sufficient to meet the fire standards may have a deleterious effect on impact resistance of copolyester film or sheet containing an effective amount of the flame retardant materials.
Copolyesters can be flame retarded in a variety of means but these methods have some drawbacks. Halogen compounds such as Declorane Plus, decabromodiphenyl oxide or decabromodiphenyl ether can be effective flame retardants, but are objectionable in the marketplace due to fears of smoke toxicity during combustion, the formation of dioxin-type compounds during combustion or bio-accumulation. Liquid phosphorous compounds such as triphenyl phosphite or triphenyl phosphate can flame retard copolyesters but at effective use levels, they plasticize and soften the copolyester thus reducing heat resistance to distortion. Solid flame retardants in the melamine and phosphorous classes can be used as well, but in the past, the concentrations needed to achieve flame retardancy have made the copolyester brittle or reduced tensile strength properties. Plastics used in interior finish applications such as wall protection products and housings for handheld and stationary appliances all have flammability requirements specified in various codes or standards. These applications also have durability or physical property requirements in addition to flammability requirements. Additionally, some building and construction and appliance applications have banned the use of halogen containing compounds. Consequently, there is a need for copolyesters used in these applications that retain physical properties and use non-halogen flame retardants.
There exists a need for an improved copolyester composition comprising non-halogen flame retardants and film or sheets which exhibit good flame resistance and impact resistance.